Jeffrey Brown

Metastable electronic states and nonlinear response for high-intensity optical pulses

In this paper we propose and demonstrate that the ultrafast nonlinear optical response of atoms may be accurately calculated in terms of metastable states obtained as solutions of the stationary Schrodinger equation including the quasi-static applied electric field. We first develop the approach in the context of an exactly soluble one-dimensional atomic model with delta-function potential, as this allows comparison between the exact ultrafast nonlinear optical response and our approximate approach, both in adiabatic approximation and beyond. These ideas are then applied to a three-dimensional hydrogen-like atom and yield similar excellent agreement between the metastable state approach and simulations of the Schrodinger equation for off-resonant excitation. Finally, our approach yields a model for the ultrafast nonlinear optical response with no free parameters. It can potentially replace the light–matter interaction treatment currently used in optical filamentation, and we present a numerical example of application to femtosecond pulse propagation.

Viewing a brief chest-compression-only CPR video improves bystander CPR performance and responsiveness in high school students: A cluster randomized trial

BACKGROUND CPR training in schools is a public health initiative to improve out of hospital cardiac arrest (OHCA) survival. It is unclear whether brief video training in students improves CPR quality and responsiveness and skills retention. OBJECTIVES Determine if a brief video is as effective as classroom instruction for chest compression-only (CCO) CPR training in high school students. METHODS This was a prospective cluster-randomized controlled trial with three study arms: control (sham video), brief video (BV), and CCO-CPR class. Students were randomized and clustered based on their classrooms and evaluated using a standardized OHCA scenario measuring CPR quality (compression rate, depth, hands-off time) and responsiveness (calling 911, time to calling 911, starting compressions within 2min). Data was collected at baseline, post-intervention and 2 months. Generalized linear mixed models were used to analyze outcome data, accounting for repeated measures for each individual and clustering by class. RESULTS 179 students (14-18 years) were consented in 7 classrooms (clusters). At post-intervention and 2 months, BV and CCO class students called 911 more frequently and sooner, started chest compressions earlier, and had improved chest compression rates and hands-off time compared to baseline. Chest compression depth improved significantly from baseline in the CCO class, but not in the BV group post-intervention and at 2 months. CONCLUSIONS Brief CPR video training resulted in improved CPR quality and responsiveness in high school students. Compression depth only improved with traditional class training. This suggests brief educational interventions are beneficial to improve CPR responsiveness but psychomotor training is important for CPR quality.

Assessment of the metastable electronic state approach as a microscopically self-consistent description for the nonlinear response of atoms

This Letter presents the first quantitative assessment of the recently proposed metastable electronic state approach (MESA) for calculation of the nonlinear optical response of noble gas atoms. Based on the single active electron potentials for several atomic species, Stark resonant states are used to extract the nonlinear polarization and ionization rates free of any additional fitting parameters. It is shown that even the simplest version of the method provides a viable, first-principle-based, and self-consistent alternative to the standard model commonly used for simulations in the field of extreme nonlinear optics.

On the convergence of quantum resonant-state expansion

Completeness of the system of Stark resonant states is investigated for a one-dimensional quantum particle with the Dirac-delta potential exposed to an external homogeneous field. It is shown that the resonant series representation of a given wavefunction converges on the negative real axis while the series diverges on the positive axis. Despite the divergent nature of the resonantexpansion, good approximations can be obtained in a compact spatial domain.

Carrier-wave shape effects in optical filamentation

Strong-field ionization in optical filaments created by ultrashort pulses with sub-cycle engineered waveforms is studied theoretically. To elucidate the physics of the recently demonstrated enhanced ionization yield and spatial control of the optical filament core in two color pulses, we employ two types of quantum models integrated into spatially resolved pulse-propagation simulations. We show that the dependence of the ionization on the shape of the excitation carrier is adiabatic in nature, and is driven by local temporal peaks of the electric field. Implications for the modeling of light-matter interactions in multicolor optical fields are also discussed.

Properties of Stark Resonant States in Exactly Solvable Systems

Properties of Stark resonant states are studied in two exactly solvable systems. These resonances are shown to form a biorthogonal system with respect to a pairing defined by a contour integral that selects states with outgoing wave boundary conditions. Analytic expressions are derived for the pseudonorm, dipole moment, and coupling matrix elements which relate systems with different strengths of the external field. All results are based on explicit calculations made possible by a newly designed integration method for combinations of Airy functions representing resonant eigenstates. Generalizations for one-dimensional systems with short-range potentials are presented, and relations are identified which are likely to hold in systems with three spatial dimensions.

Viewing an ultra-brief chest compression only video improves some measures of bystander CPR performance and responsiveness at a mass gathering event

BACKGROUND CPR training at mass gathering events is an important part of health initiatives to improve cardiac arrest survival. However, it is unclear whether training lay bystanders using an ultra-brief video at a mass gathering event improves CPR quality and responsiveness. OBJECTIVE To determine if showing a chest-compression only (CCO) Ultra-Brief Video (UBV) at a mass gathering event is effective in teaching lay bystanders CCO-CPR. METHODS Prospective control trial in adults (age >18) who attended either a womens University of Arizona or a mens Phoenix Suns basketball game. Participants were evaluated using a standardized cardiac arrest scenario with Laerdal Skillreporter™ mannequins. CPR responsiveness (calling 911, time to calling 911, starting compressions within two minutes) and quality (compression rate, depth, hands-off time) were assessed for participants and data collected at Baseline and Post-intervention. Different participants were tested before and after the exposure of the UBV. Data were analyzed via the intention to treat principle using logistic regression for binary outcomes and median regression for continuous outcomes, controlling for clustering by venue. RESULTS A total of 96 people were consented (Baseline=45; Post intervention=51). CPR responsiveness post intervention improved with faster time to calling 911 (s) and time to starting compressions (sec). Likewise, CPR quality improved with deeper compressions and improved hands-off time. CONCLUSIONS Showing a UBV at a mass gathering sporting event is associated with improved CPR responsiveness and performance for lay bystanders. This data provides further support for the use of mass media interventions.

Modeling of ultrafast laser pulse propagation

Computer simulations of ultrafast optical pulses face multiple challenges. This requires one to construct a propagation model to reduce the Maxwell system so that it can be efficiently simulated at the temporal and spatial scales relevant to experiments. The second problem concerns the light-matter interactions, demanding novel approaches for gaseous and condensed media alike. As the nonlinear optics pushes into new regimes, the need to honor the first principles is ever greater, and requires striking a balance between computational complexity and physical fidelity of the model. With the emphasis on the dynamics in intense optical pulses, this paper discusses some recent developments and promising directions in the field of ultrashort pulse modeling.

SMA actuators: a viable practical technology (Presentation Video)

Diverse products either based solely on or incorporating Shape Memory Alloys (SMA) have and are being made in a wide range of industries, and IP is being captured. Why then compared to SE (superelastic) Nitinol, and especially conventional technology, do so few ideas reach production? This presentation delves deeply into this topic in reaching the final assessment that SMA actuators are indeed now a viable practical technology. The presentation begins with an introduction to and description of the fundamental basis of SMA actuator technology. Examples of multiple commercially available geometric forms of SMA actuators are given and the functionalities that they provide are described. This is followed by examples of multiple commercial products incorporating such SMA actuators. Given that there are literally millions of commercial products incorporating conventional actuator technologies, indications are given as to why there are their less than 1000 that utilize SMA. Experience based challenges to the commercial use of SMA actuators are described. Besides having to compete with existing non-SMA technology which is quite mature additional challenges that are unique to SM actuators are indicated these including a wider than expected set of technical engineering problems and challenges and that a broader scope of dynamics is required.

Ultrafast light-matter coupling in condensed and gaseous nonlinear media

After a brief historical review, we describe recent research in the study of tera-Watt class femtosecond lasers propagating in air and condensed media. Here critical self-focusing of the light field reflects the presence of a famous singularity (blow-up in finite time) in the governing Nonlinear Schrö dinger equation (NLS) — this contribution deals with moving into a regime where NLSE fails and more exact optical carrier resolved pulse propagators need to be developed and secondly, addresses the failure of well-established phenomenological nonlinear optical susceptibilities and their replacement by more fundamental quantum models.